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• Decoding a h264 (High) stream with OpenCV's ffmpeg on Ubuntu

  5 juin 2018, par arvids

  I am working with a video stream from an ip camera on Ubuntu 14.04. Everything was going great with a camera that has these parameters (from FFMPEG) :

      Stream #0:0: Video: h264 (Main), yuv420p(progressive), 352x192, 29.97 tbr, 90k tbn, 180k tbc

  But then i changed to a newer camera, which has these parameters :

      Stream #0:0: Video: h264 (High), yuvj420p(pc, bt709, progressive), 1280x720, 25 fps, 25 tbr, 90k tbn, 50 tbc

  My C++ program uses OpenCV3 to process the stream. By default OpenCV uses ffmpeg to decode and display the stream with function VideoCapture.

  VideoCapture vc;
  
  vc.open(input_stream);
  
  while ((vc >> frame), !frame.empty()) {
  
     *do work*
  
  }

  With the new camera stream i get errors like these (from ffmpeg) :

  [h264 @ 0x7c6980] cabac decode of qscale diff failed at 41 38
  
  [h264 @ 0x7c6980] error while decoding MB 41 38, bytestream (3572)
  
  [h264 @ 0x7c6980] left block unavailable for requested intra mode at 0 44
  
  [h264 @ 0x7bc2c0] SEI type 25 truncated at 208

  The image sometimes is glitched, sometimes completely frozen. However on vlc it plays perfectly. I installed the newest version (3.2.2) of ffmpeg player with

  ./configure --enable-gpl --enable-libx264

  Now playing directly with ffplay (instead of launching from source code with OpenCV function VideoCapture), the stream plays better, but sometimes still displays warnings :

  [NULL @ 0x7f834c008c00] SEI type 25 size 896 truncated at 320=1/1   
  
  [h264 @ 0x7f834c0d5d20] SEI type 25 size 896 truncated at 319=1/1   
  
  [rtsp @ 0x7f834c0008c0] max delay reached. need to consume packet   
  
  [rtsp @ 0x7f834c0008c0] RTP: missed 1 packets
  
  [h264 @ 0x7f834c094740] concealing 675 DC, 675 AC, 675 MV errors in P frame

  Changing the camera hardware is not an option. The camera can be set to encode to h265 or mjpeg. When encoding to mjpeg it can output 5 fps, which is not enough. Decoding to a static video is not an option either, because i need to display real time results about the stream. Here is a list of API backends that can be used in function VideoCapture. Maybe i should switch to some other decoder and player ?
  From my research i conclude that i have these options :

  • Somehow get OpenCV to use libVlc instead of ffmpeg

  One example of switching to vlc is here, but i don’t understand it well enough to say if that is what i need. Or maybe i should be parsing the stream in code ?

  • Use vlc to preprocess the stream, as suggested here.

  This is probably slow, which again is bad for real time results.
  Any suggestions and coments will be appreciated.

• What is the difference between ffmpeg command with -codec and without -codec

  26 avril 2018, par Sat

  I am trying to calculate video frozen time, I created mp4 format file with 23seconds frozen.
  I am converting mp4 file into segment(.ts) file using following command

  ffmpeg -i Palivala.mp4 -codec copy -vbsf h264_mp4toannexb -map 0 palivaalaa.ts

  When i directly use video file (Palivala.mp4) or segment file(palivaalaa.ts) which generated from above command, I am getting the result as expected. i.e getting video frozen time as 23seconds.

  But when I use following command

  ffmpeg -i Palivala.mp4  -map 0 palivaalaa.ts

  I am able to see 1second frozen frames then after that 1 frame without frozen immediately next frame frozen and frozen continued for 6seconds again 1 non-frozen frame...................

  1) What is the difference between above 2 commands ?

  2) both commands chooses libx264 ?

• Append black frames to video when audio is longer in ffmpeg

  8 avril 2018, par Edward

  I’m trying to utilize ffmpeg as a video editor and this is mostly due to that the regular video editor dropped more frames than I was comfortable with.

  ffmpeg -i "videoplayback1" -t 00:09:51 -i "audioplayback1" -t 00:09:54.38 -vcodec libx264 -crf 20 -acodec copy "playback1.mp4"

  As you can see, I’m trimming the video shorter than the audio, but what I want is something that is the opposite of the -shortest command switch, to have the file continue for the duration of the audio -t, and adding physical black frames for the remainder of that time.

  As it is now, the video is still clipped as if I was using the -shortest switch. I tried some -vf and filter_complex but either I get errors, or that the audio is still chopped, the video frozen, but the duration is that of the longest -t.

  How would I go about adding black frames for as long as the audio is playing ?